Prior Coriolis effect densimeters, such as that disclosed in the U.S. Pat. No. 4,876,879 to Ruesch of Oct. 31, 1989, were designed and operated with the assumption that the accuracy of the density measurement is not affected by changes in the mass flow rate, temperature, viscosity or pressure of the measured fluid. In particular, these densimeters were designed with the assumption that changes in the natural frequency of the driven flow tubes are only caused by changes in the density of the material flowing through the flow tube. The density measurement was determined by these meters directly from the measured natural frequency.
Each Coriolis effect densimeter has a specified set of recommended operating parameters such as temperature, mass flow rate, density, viscosity, pressure, etc. Coriolis effect meters designed in accordance with these assumptions have operated satisfactorily and given excellent results for most users when their recommended operating ranges are not exceeded. These meters then normally yield excellent performance coupled with a high precision of output data.
However, circumstances occur in which a Coriolis effect densimeter may be operated beyond its recommended operating range or near the upper limits of the recommended operating range of flow rates. Under these conditions, the accuracy of the output data is decreased somewhat as compared to the accuracy of the output data usually obtained when the meters are operated within their recommended operating ranges.
Heretofore, when a user required higher mass flow rates, she or he was required to switch to a higher capacity Coriolis meter in order to operate the flowmeter with an acceptable pressure drop. However, advances in the design of Coriolis mass flowmeters have resulted in lower pressure drops which have effectively broadened the useful range of the flowmeter. Users operating their flowmeters over this extended range, which may exceed the previously recommended range, may obtain output data that is not of the highest possible accuracy.